I\    II,    T   "T^ 


Issued  November  30,  1909 


U.  S.  DEPARTMENT  OF  AGRICULTURE, 

BUREAU  OF  PLANT  [NDUSTRY— Circular  No.  10. 

B.  T.  QALLOWAY,  Chief  of  Bureau. 


A  SIMPLE  METHOD  OF  DETECTING  SULPHURED 
BARLEY  AND  OATS. 


W.  P.  CARROLL, 

Assistant  in  Charge  of  the  Chicago  Grain 
Standardization  Laboratory. 


WASHINGTON  :  GOVERNMENT  PRINTING  OFFICE  :  1909 


[Cir.  40] 
2 


BUREAU  OF  PLANT  INDUSTRY. 


flu,/  of  Bureau,  Beverly  T.  Galloway. 
Assistant  Chief  of  Bureau,  Albert  F.Woods. 
Editor,  J.  E.  Rockwell. 
Chief  Clerk,  James  E.  Junks. 


B.  P.  I.—. ".JO. 


A  SIMPLE  METHOD  OF  DETECTING  SUL- 
PHURED  BARLEY  AND  OATS. 


INTRODUCTION. 

For  years  it  has  been  the  common  practice  in  some  grain  centers  to 
subjeel  stained  or  discolored  barley  and  oats  to  a  process  of  bleaching 
in  order  to  remove,  oral  least  partially  remove,  the  discoloration  and 
to  a  certain  extent  improve  the  appearance  of  kernel-  otherwise  dam 
aged.  The  common  agent  to  accomplish  this  result  is  sulphur  in  the 
form  of  sulphurous  acid,  and  the  process  itself  is  known  by  different 
names,  among  which  are  the  terms  "sulphuring,"  " bleaching,"  and 
••  purify  ing." 

The  general  appearance,  especially  the  color,  of  barley  and  oats, 
has  an  important  bearing  in  determining  their  commercial  grade-  and 
values,  and  in  view  of  the  fact  that  the  bleaching  of  these  grains  has 

bee ■  '.minion,  and  liecause  it  is  oftentimes  difficult  to  discriminate 

between  -rain  that  has  been  bleached  and  grain  that  is  naturally 
bright  in  appearance,  it  was  deemed  expedient  to  use  a  simple  qualita- 
tive method  by  means  of  which  the  grain  merchant  or  grain  inspector 
could  determine  whether  or  not  grain  has  been  sulphured.  Hereto- 
fore 1 1  it  sense  of  smell  or  the  personal  judgment  has  been  the  only 
means  available  to  practical  grain  men  of  differentiating  between  the 
natural  and  the  bleached  grains. 

METHOD  OF  BLEACHING  USED. 

Sulphur  burned  in  air  or  in  the  presence  of  0x3  gen  becomes  sulphur 
dioxid.  a  colorless,  t  transparent  gas  with  a  sharp,  pungent  odor  similar 
to  that  found  in  burning  sulphur  matches.     This  gas  is  verj  soluble 

in  water,  forming  sulphurous  acid,  which  is  the  bleaching  agent  for 
barley  and  oats. 

In  actual  practice,  the  sulphur  is  changed  to  sulphur  dioxid  by  burn- 
ing in  an  o\  en.  from  w  hich  the  funics  are  conducted  to  a  receptacle  or 
bleaching  tower,  from  the  bottom  to  the  top  of  which  the  gas  circu- 
lates, coming  in  contact  with  the  grain  that  is  constantly  passing 
through  the  tower.  Water  must  be  supplied  to  change  the  dioxid  into 
sulphurous  acid,  as  sulphur  dioxid  is  not  a  bleaching  agent.  This  is 
[Cir.  40] 


4  METHOD    OF    DETECTING    SULPHURED     BARLEY    AND    OATS. 

done  by  dampening  the  grain  either  with  steam  or  small  sprays  of 
water  playing-  upon  the  grain  as  it  enters  the  tower. 

The  bleaching  is  supposedly  bi'ought  about  by  the  acid  abstracting 
oxygen  from  the  coloring  matter  of  the  grain.  Complete  bleaching  is 
not  immediate,  and  the  grain  is  therefore  conveyed  in  a  damp  condition 
from  the  bleaching  apparatus  to  moderately  air-tight  bins,  where  it  is 
allowed  to  remain  long  enough  to  finish  the  process.  To  prevent  heat- 
ing and  to  put  the  grain  in  a  proper  condition  for  shipping,  it  is  moved 
about  after  some  time  in  such  a  manner  as  will  permit  the  air  to  pass 
freely  through  it,  which  to  a  certain  extent  will  remove  the  acid  odor 
but  will  not  completely  remove  all  of  the  sulphurous  acid,  the  presence 
of  which  will  always  betray  the  fact  that  the  grain  has  been  "sul- 
phured." 

The  method  outlined  in  this  circular  for  the  detection  of  sulphur- 
ous acid  has  been  one  of  the  standard  methods  of  ascertaining  the 
presence  of  sulphurous  acid  in  grain  for  several  years,  and  a  more 
detailed  description  of  the  chemical  reactions  that  take  place  may  be 
found  in  any  of  the  later  standard  text-books  on  qualitative  chemistry. 
The  principle  upon  which  the  method  is  based  is  to  change  sulphurous 
acid  into  hydrogen  sulphid,  which  in  the  presence  of  lead  salt  will 
give  a  brownish  black  precipitate.  This  method  has  been  used  in 
Germany  for  some  years  in  detecting  sulphurous  acid  in  bleached 
seeds,  and  in  modified  forms  by  chemists  in  this  country  for  similar 
purposes.  In  order  to  accelerate  the  test  and  at  the  same  time  reduce 
the  possibility  of  error  to  a  minimum,  so  that  it  can  be  used  by  per- 
sons other  than  those  familiar  with  chemical  reactions,  it  has  been 
deemed  advisable  to  make  a  few  changes  in  the  apparatus  commonly 
used. 

THE  CHEMICALS  NECESSARY  FOR  DETECTING  SULPHURED 

GRAIN. 

For  the  detection  of  sulphured  grain  a  supply  of  chemically  pure 
zinc,  hydrochloric  acid,  lead  acetate,  ferric  or  platinic  chlorid,  and 
distilled  water  should  always  be  on  hand.  The  hydrochloric  acid 
should  be  diluted  to  about  20  per  cent  of  its  normal  strength  by  add- 
ing 4  parts  of  distilled  water  to  1  part  of  acid.  The  lead  acetate 
must  be  dissolved  in  water,  and  to  give  the  best  results  the  solution  is 
prepared  by  adding  2  grams  of  the  acetate  for  every  98  cubic  centi- 
meters of  distilled  water,  which  makes  practically  a  2  per  cent  solution. 

If  the  operator  desires  to  make  several  tests,  stock  solutions  of  the 
proper  strength  should  be  made  up  in  quantity.  However,  if  the 
stock  solution  of  lead  acetate  is  allowed  to  stand  very  long  it  will 
become  scummy  and  flakes  will  adhere  to  the  sides  of  the  container. 
Therefore,  it  will  be  necessaiy  to  filter  it  occasionally  so  that  a  clear, 
transparent  liquid  may  always  be  ready  for  use  when  needed. 

[Cir.  40] 


METHOD    OF    DETECTING    BULPHUBED    BARLEY    AND    OATS. 


METHOD  OF  TESTING  GRAIN.' 


To  perform  the  test,  LO  grams  of  chemically  pure,  moss}',  granular, 
or  shot  zinc  are  distributed  over  the  bottom  of  a  glass  container  \\  ith 
:i  capacity  of  al  least  500  cubic  centimeters.  Upon  the  zinc  are  pi 
about  l"1'  grams  of  the  grain  t<»  be  tested.  Into  the  Bask  is  poured 
enough  dilute  hydrochloi  ic  acid  to  cover  the  grain,  approximately  LOO 
cubic  centimeters.  The  Hash  is  then  closed  with  a  cork  stopper  pro 
vided  with  an  inverted  "  L"  glass  tube  about  7  millimeters  in  internal 
diameter.  The  short  arm  of  the  glass  tube  should  project  approxi- 
mately one  halt'  inch  Kclow  the  bottom  of  the  stopper,  while  the  long 
arm  should  extend  nearly  to  the  bottom  of  the  test  tube  containing  a 
2  per  cent  solution  of  lead  acetate.  (See  fig.  I.)  A  test  tube  of  about 
15  cubic  centimeters  capacity  is  large  enough  tor  this  purpose  and 
should  ii"t    he  over  two-thirds  full;  otherwise  the  contents  "will  spill 


Fig.  1. — Chemicals  and  apparatus  used  for  detecting  sulphured  grain. 

over  as  soon  a-  the  gas  begins  to  pass  freely  from  the  zinc  and  the 
hydrochloric  acid.     If  the  zinc  is  very  pure     that  is  to  say,  free  from 
all  foreign  substances     the  action  between  the  zinc  and  the  hydro 
chloric  acid  will  be  retarded,  but  it  may  be  considerably  hastened  by 
the  addition  of  a  few  drops  of  ferric  chlorid.     On  the  left  in  figure  1 

In  Bulletin  107  (revised  .  Bureau  of  Chemistry,  I'.  S.  Dcpt.  of  Agriculture,  p. 
is:,  the  use  <>f  a  lead  -alt  in  a  little  different  form  is  recommended  for  the  detection 
of  sulphurous  acid  in  vegetables.  This  test  is  commonly  known  as  the  Lead-paper 
tesl  and  differs  from  the  solution  test  described  in  this  circular  in  thatapii 
bibulous  paper  is  saturated  with  a  solution  of  a  lead  salt  and  is  then  placed  under- 
neath the  stopper  of  the  flask  in  which  the  hydrogen  i-  generated  instead  of  using 
id  solution  in  a  separate  compartment.  The  lead-paper  test  bas  been  used  by 
some  ,  hemists  tor  tin-  d.  tei  tion  of  sulphurous  acid  in  grain,  and  it  was  also  tried  in 
the  Bureau  of  Planl  tudustr)  for  the  same  purpose,  hut  after  repeated  trials  it  was 

ii. .t  deemed  advisable  to  recoi end  its  use  by  persons  unfamiliar  with  chemical 

reactions. 

[Cir.  40] 


6         METHOD    OF    DETECTING    SULPHURED    BARLEY    AND    OATS. 

are  shown  two  flasks  with  connections  to  the  test  tubes.  This  figure 
fully  demonstrates  how  the  apparatus  is  to  be  adjusted. 

When  the  hydrochloric  acid  comes  in  contact  with  the  zinc  in  the 
bottom  of  the  flask,  hydrogen  is  liberated  and  bubbles  may  be  noticed 
passing  up  through  the  grain  and  then  through  the  lead  acetate  in  the 
test  tube.  As  soon  as  the  air  has  been  expelled  from  the  flask,  these 
bubbles  are  either  hydrogen  or  hydrogen  sulphid,  conditional  upon 
whether  the  grain  is  natural  or  sulphured.  With  unbleached  grain 
the  gas  is  hydrogen  and  the  bubbles  passing  through  the  lead  acetate 
solution  will  leave  the  liquid  in  the  tube  clear,  colorless,  and  trans- 
parent, but  with  sulphured  grain  these  bubbles  will  be  hydrogen  sul- 
phid gas,  which  produces  a  brownish  black,  flocculent  precipitate  in 
the  lead  acetate.  This  precipitate  is  lead  sulphid,  caused  by  the 
breaking  up  of  the  hydrogen  sulphid  and  the  lead  acetate,  the  lead 
of  the  latter  uniting-  with  the  sulphur  of  the  former. 

Occasionally  fine  granules  will  be  seen  held  in  suspension  in  the  lead 
acetate  should  the  grain  be  very  dusty,  and  the  same  conditions  will 
exist  if  the  acid  is  too  strong,  because  strong  acid  produces  violent 
action  in  the  flask,  which  may  cause  to  be  carried  over  some  tine  parti- 
cles of  dust  or  zinc.  These  granules  must  not  be  mistaken  for  lead 
sulphid.  After  the  operator  has  had  a  little  experience  he  can  readily 
distinguish  the  granules  from  the  black,  flocculent  precipitate.  It  is 
easy  to  test  these  granules  by  adding  a  few  drops  of  ferric  chlorid 
(one  part  of  ferric  chlorid  dissolved  in  ten  parts  of  distilled  water)  to 
the  precipitate  in  the  test  tube.  If  the  precipitate  is  lead  sulphid  it 
will  readily  dissolve  in  the  ferric  chlorid,  whereas  the  zinc  particles 
and  dust  will  remain  practically  unchanged.  These  particles  and  their 
consequent  annoyance  ma}r  be  obviated  to  a  great  extent  by  screening 
the  grain  before  it  is  put  into  the  flask.  A  still  better  way,  however, 
to  circumvent  this  difficulty  is  to  place  a  piece  of  clean  absorbent 
cotton  in  the  neck  of  the  flask  just  below  the  outlet  in  the  stopper, 
which  will  serve  as  a  filter  and  allow  the  gas  to  pass  through  freely, 
but  will  retain  any  solid  impurities  that  may  come  in  contact  with  it. 

NECESSITY  FOR  CLEANLINESS. 

In  all  cases  mixing  pans,  glassware,  and  all  other  apparatus  should 
be  clean,  and  no  chemicals  should  be  used  that  are  not  chemically  pure. 
These  precautions  can  not  be  urged  or  impressed  too  strongly  upon 

tl perator,  because  other  substances  might  be  present  in  the  glass- 

w.ue  and  chemicals  that-  would  perhaps  give  a  reaction  similar  to  that 
of  sulphurous  acid.  Rubber  stoppers  contain  sulphur  in  their  com- 
position, although  not  in  such  a  form  that  it  is  readily  changed  to 
hydrogen  sulphid;  still,  it  is  advisable  to  use  cork  stoppers  to  avoid 
any  possibility  of  doubt  or  controversy.  Flasks  with  ground-glass 
stoppers,  provided  with  special  conducting  tubes,  are  to  be  preferred 
in  all  cases  when'  they  are  procurable. 
[Cir.  lu] 


METHOD    OF    DETECTING    SULPHURED    BARLEY     ANI>    OATS.  7 

TESTS  OF  NATURAL  BARLEY  IN  COMPARISON  WITH  SULPHURED 

BARLEY-. 

There  seems  to  be  a  difference  of  opinion  among  persons  engaged 
in  the  grain  trade  as  i<>  whether  the  precipitate  of  lead  sulphid  is  pro- 
cured onlj  Prom  grain  that  has  been  sulphured.  Some  contend  that 
the  natural  sulphur  found  in  barley  rich  in  protein  will  give  the  same 
precipitate  as  thai  found  in  sulphured  barley  and  furthermore  that 
i li ill 'ii 'ni  soils  will  produce  barley  some  of  which  will  show  a  sulphur 
reaction.  It  may  be  said,  however,  in  this  connection,  that  the  natural 
sulphur  found  in  the  protein  of  200  or  300  grams  of  barley  is  too  small 
to  manifesl  itself  in  such  a  test,  because  the  dilute  acid  has  hardly 
sufficient  time  to  penetrate  the  interior  of  the  kernel-.  Moreover, 
facts  do  nol  bear  out  these  contentions,  as  will  be  demonstrated. 

To  ascertain  how  barley  grown  on  different  .-oils  and  in  different  sec- 
tions of  the  country  would  respond  when  subjected  to  the  test  described 


Fig.  2     E  led  with  solutions,  showing  the  results  of  tests  of  sulphured  commercial  barley 

(A)  and  of  pure  unsulphured  barley  (B)  received  from  tin'  agricultural  experiment  s( 
Minnesol  i,  Nebraska,  Iowa,  Wisconsin,  Utah,  Kansas,  and  Indiana. 

in  this  circular,  requests  were  made  to  the  agricultural  experiment 
stations  ><(  Minnesota,  Nebraska,  Iowa.  Wisconsin,  Utah,  Kansas,  aid 
Indiana  for  barley  samples  that  were  know  u  to  lie  unsulphured.  Each 
of  these  stations  forwarded  -ample-  and  a  qualitative  test  of  each  was 
made.  Four  ounce-  of  lead  acetate  were  used  instead  of  L0  cubic 
centimeters,  L, 000  grams  of  barley  were  substituted  for  LOO  grams  in 
each  case,  and  the  acid  and  zinc  were  increased  in  the  same  proportion. 
In  figure  •_'  the  solution  in  the  bottle  on  the  left  is  of  inky  blackness 
in  color,  indicating  a  heavy  precipitate  of  lead  sulphid.  The  barley 
which  caused  this  discoloration  was  known  to  he  sulphured.  The 
hydrogen  which  passed  through  the  solutions  of  the  remaining  seven 
bottles  was  generated  in  the  presence  of  the  natural  hurley  from 
Minnesota,  Nebraska,  fowa,  Wisconsin,  Utah,  Kansas,  and  Indiana, 
respectively,  bul  the  liquid  remained  clear  ami  transparent. 

[Cir.  in] 


0         METHOD    OF    DETECTING    SULPHURED    BARLEY    AND    OATS. 

The  bottle  marked  A  on  the  left  in  figure  3  shows  the  result  obtained 
by  generating  hydrogen  in  the  presence  of  commercially  sulphured 
barley  and  allowing  the  gas  to  pass  through  a  solution  of  lead  acetate, 
as  in  the  qualitative  test  herein  described.  The  bottles  marked  7?', 
C".  and  //.show  the  results  of  similar  tests  with  natural  barley  from 
the  agricultural  experiment  stations  of  Nebraska,  Wisconsin,  and 
Kansas,  respectively,  while  those  marked  B,  C,  and  D  are  from  the 
same  stations,  but  have,  respectively,  50  per  cent,  25  per  cent,  and  2£ 
per  cent  of  sulphured  barley  added. 

The  contrast  between  the  precipitate  in  the  two  bottles  of  each  pair 
is  readily  apparent.  The  lead  sulphid  is  so  abundant  in  A,  which 
represents  a  commercially  sulphured  sample,  that  the  whole  solution 


— 

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Fig.  3.— Seven  bottles  tilled  with  solutions,  showing  the  results  of  tests  of  samples  containing  differ- 
ent percentages  of  sulphured  barley  and  of  samples  of  natural,  or  unsulphured,  barley  from  the 
agricultural  experiment  stations  of  Nebraska,  Wisconsin,  and  Kansas. 

is  Mack  and  opaque.  The  solutions  in  B,  (',  and  D  vary  from  black 
turbidity  to  dull  translucency,  depending  upon  the  percentage  of 
sulphured  barley.  Contrasted  with  the  natural  barley  in  each  case, 
the  turbidity  is  very  evident,  and  it  is  plainly  seen  that  this  turbidity 
decreases  from  right  to  left,  or  as  the  percentage  of  sulphured  admix- 
ture decreases.  Numerous  other  trials  were  made  with  sulphured 
and  unsulphured  grain,  and  in  each  case  the  same  results  were 
obtained. 
A  pproved: 

James  Wilson, 

Secretanj  of  Agriculture. 

Washington,  I).  C.  October  1.1,  l!>09. 

[Cir.  40] 

o 


